Air conditioner and method of controlling such

ABSTRACT

The object of this invention is to provide an air conditioner with a variable capacity compressor ( 2 ) parallely connected to a fixed capacity compressor ( 4 ), and a method of controlling the operation of such an air conditioner. When it is required to start the fixed capacity compressor ( 4 ) in addition to an operation of the variable capacity compressor ( 2 ) due to an increase in the sum of the required cooling capacities of indoor units ( 9 ), an outdoor control unit ( 13 ) starts the fixed capacity compressor ( 4 ) during an unloading mode operation of the variable capacity compressor ( 2 ) where the pressure difference between the outlet side and inlet side of the variable capacity compressor is minimized. The fixed capacity compressor ( 4 ) is thus smoothly started without causing an induction of excessive starting current, and improves the operational reliability of the air conditioner.

TECHNICAL FIELD

[0001] The present invention relates, in general, to air conditionersand a method of controlling such air conditioners and, moreparticularly, to an air conditioner with a variable capacity compressorand a fixed capacity compressor, and a method of controlling theoperation of such an air conditioner by operating the fixed capacitycompressor in consideration of the operational condition of the variablecapacity compressor.

BACKGROUND ART

[0002] In accordance with the recent trend of up-scale of buildings,consumer's requirements for multi-air conditioners with several indoorunits commonly connected to one outdoor unit have increased. In amulti-air conditioner, the required cooling capacities of the indoorunits are different from each other and the indoor units areindependently operated, and so the total cooling capacity of the airconditioner, which is calculated by the sum cooling capacities of theindoor units, is also variable. It is thus necessary to control thecapacity of a compressor and control the opening ratio of the electricexpansion valve, installed at the upstream of an evaporator used as aheat exchanger of each indoor unit, in accordance with a variation inthe total cooling capacity of the air conditioner.

[0003] In order to accomplish the variable cooling capacity of suchmulti-air conditioners, variable capacity compressors with variablerefrigerant compressing capacity have been used. Such variable capacitycompressors are typically classified into two types: variable rpmcompressors and pulse width modulation compressors. In a variable rpmcompressor, the motor's rpms are controlled in accordance with avariation in the sum of the required cooling capacities of indoor unitsby changing, through an inverter control, the frequency of the currentapplied to the compressor. The capacity of the variable rpm compressoris thus controlled and accomplishes the variable cooling capacity in amulti-air conditioner. In a pulse width modulation compressor, thecapacity of the compressor is controlled in response to a duty controlsignal which determines the loading time when the compressor dischargescompressed refrigerant and the unloading time when the compressor ceasesto discharge compressed refrigerant. The pulse width modulationcompressor thus accomplishes the variable cooling capacity of amulti-air conditioner.

[0004] However, the variable capacity of such compressors typically usedin multi-air conditioners is limited. During the operation of such amulti-air conditioner, the sum of the required cooling capacities of theindoor units, which are commonly connected to one outdoor unit, mayexceed the capacity of one variable capacity compressor installed in theair conditioner. Therefore, it is necessary to install an additionalvariable capacity compressor in the air conditioner.

[0005] However, such variable capacity compressors are expensive anddifficult to install in multi-air conditioners in comparison with fixedcapacity compressors which have fixed refrigerant compressing capacity.Therefore, in the prior art, both a variable capacity compressor and afixed capacity compressor are installed in a multi-air conditioner andare parallely connected to each other in order to meet the demands ofthe variable cooling capacities of the indoor units.

[0006] In the operation of a multi-air conditioner with two such typesof compressors, the cooling operation of the indoor units is performedby using only the variable capacity compressor when the sum of therequired cooling capacities of the indoor units varies within theallowable capacity range of the variable capacity compressor. When thesum of the required cooling capacities of the indoor units exceeds thecapacity of the variable capacity compressor, the fixed capacitycompressor is operated at the same time to meet the required coolingcapacities of the indoor units.

[0007] However, the conventional multi-air conditioner with bothcompressors is designed such that the fixed capacity compressor isstarted regardless of the operational condition of the variable capacitycompressor, and so an excessive starting current may be induced in thefixed capacity compressor. Such a starting current prevents the smoothstart of the fixed capacity compressor, and reduces the startingperformance of said compressor. Furthermore, the excessive startingcurrent sometimes damages the fixed capacity compressor, and causes areduction in the operational reliability of the air conditioner.

DISCLOSURE OF THE INVENTION

[0008] Accordingly, the present invention has been made keeping in mindthe above problems occurring in the prior art, and an object of thepresent invention is to provide an air conditioner with a variablecapacity compressor and a fixed capacity compressor, and a method ofcontrolling the operation of such an air conditioner by operating thefixed capacity compressor in consideration of the operational conditionof the variable capacity compressor, thus accomplishing the smooth startof the fixed capacity compressor.

[0009] In order to accomplish the above object, the present inventionprovides an air conditioner, comprising: a fixed capacity compressorwith fixed refrigerant compressing capacity; a variable capacitycompressor operated in a loading mode for discharging refrigerant and inan unloading mode for ceasing to discharge refrigerant, with refrigerantcompressing capacity of the variable capacity compressor varying inresponse to a duty control signal which determines a loading time and anunloading time within a cycle; and a control unit starting the fixedcapacity compressor and the variable capacity compressor with adifference in time so as to prevent a synchronous start of the fixedcapacity compressor and the variable capacity compressor.

[0010] In the above air conditioner, the control unit starts the fixedcapacity compressor after starting the variable capacity compressor.

[0011] The control unit also starts the fixed capacity compressor suchthat the total current, which is the sum of a starting current of thefixed capacity compressor and an operating current of the variablecapacity compressor, does not exceed a maximum allowable current.

[0012] The control unit also starts the fixed capacity compressor duringan unloading mode operation of the variable capacity compressor when itis required to start the fixed capacity compressor.

[0013] In the case of the variable capacity compressor constantlymaintaining a loading mode even though it is required to start the fixedcapacity compressor, the control unit forcibly converts the loading modeof the variable capacity compressor into an unloading mode, and startsthe fixed capacity compressor after the mode conversion.

[0014] The present invention also provides a method of controlling anair conditioner consisting of a fixed capacity compressor with fixedrefrigerant compressing capacity, and a variable capacity compressorbeing varied in refrigerant compressing capacity in response to a dutycontrol signal determining a loading time and an unloading time within acycle, wherein the method comprises the steps of: starting the variablecapacity compressor; determining whether it is required to start thefixed capacity compressor in addition to an operation of the variablecapacity compressor; and starting the fixed capacity compressor inaccordance with an operational condition of the variable capacitycompressor when it is required to start the fixed capacity compressor.

[0015] In the above method, the step of starting the fixed capacitycompressor comprises the steps of: determining whether the variablecapacity compressor is operating in an unloading mode; and starting thefixed capacity compressor under the condition that the variable capacitycompressor is operating in an unloading mode.

[0016] The step of starting the fixed capacity compressor may comprisethe step of: starting the fixed capacity compressor after waiting for aconversion in the operational mode of the variable capacity compressorfrom a loading mode into an unloading mode when the variable capacitycompressor is being operated in the loading mode.

[0017] The step of starting the fixed capacity compressor may comprisethe step of: starting the fixed capacity compressor after forciblyconverting an operational mode of the variable capacity compressor froma loading mode into an unloading mode when the variable capacitycompressor is continuously operated in the loading mode.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The above and other objects, features and other advantages of thepresent invention will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings, in which:

[0019]FIG. 1 is a circuit diagram showing the refrigeration cycle of theair conditioner according to the primary embodiment of the presentinvention;

[0020]FIG. 2 is a view showing a relationship between the loading andunloading times and the amount of refrigerant discharged from thecompressor of this invention;

[0021]FIG. 3 is a block diagram showing the construction of the controlsystem of the air conditioner according to this invention;

[0022]FIGS. 4a and 4 b are graphs showing the induction of an excessivecurrent in the fixed capacity compressor by operation of the variablecapacity compressor and the fixed capacity compressor at the same time;

[0023]FIGS. 5a and 5 b are graphs showing the operation of the airconditioner, according to the present invention, which controls thefixed capacity compressor in consideration of the operational conditionof the variable capacity compressor; and

[0024]FIG. 6 is a flowchart of the control method of the outdoor controlunit included in the air conditioner according to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

[0025] Reference now should be made to the drawings, in which the samereference numerals are used throughout the different drawings todesignate the same or similar components.

[0026]FIG. 1 is a circuit diagram showing the refrigeration cycle of themulti-air conditioner according to the preferred embodiment of thepresent invention.

[0027] As shown in the drawing, the multi-air conditioner of thisinvention comprises one outdoor unit 1 and a plurality of indoor units9. The outdoor unit 1 includes a variable capacity compressor 2, a fixedcapacity compressor 4, and a condenser 5. The two compressors 2, 4 areparallely connected to each other. The variable capacity compressor 2 isa pulse width modulation compressor, which is operated in a loading modefor discharging refrigerant and an unloading mode for not dischargingrefrigerant. A PWM valve 3 controls the loading and unloading modeoperation of the variable capacity compressor 2. The fixed capacitycompressor 4 is a general type compressor, which is selectively operatedby being electrically turned on or off, and is rotated at a constantrpm.

[0028] The indoor units 9 are parallely connected to the outdoor unit 1,and each include an evaporator 10 and an electric expansion valve 12. Ina brief description, the multi-air conditioner has an arrangementconsisting of the parallel connection of several indoor units 9 to oneoutdoor unit 1. The capacities and types of the indoor units 9 may beequal to or different from each other without affecting the functioningof this invention.

[0029] In the outdoor unit 1, the variable capacity compressor 2 and thefixed capacity compressor 4 are parallely connected to each otherbetween the high pressure outlet pipe 6 and the low pressure inlet pipe7. The high pressure outlet pipe 6 is a refrigerant outlet pipe whichguides discharged refrigerant from the compressors 2, 4 to the condenser4. The low pressure inlet pipe 7 is a refrigerant inlet pipe whichguides refrigerant from the evaporators 10 of the indoor units 9 to thetwo compressors 2 and 4.

[0030] As shown in FIG. 2, the variable capacity compressor 2alternately performs the loading mode operation with the PWM valve 3turned off to discharge refrigerant, and the unloading mode operationwith the PWM valve 3 turned on to cease to discharge refrigerant. In theoperation of such a compressor 2, the loading and unloading time variesin response to a duty control signal applied to an outdoor control unitin accordance with the sum of the required cooling capacities of theindoor units 9. The outdoor control unit will be described in detaillater herein. The shaded surface areas in FIG. 2 indicate the amounts ofdischarged refrigerant.

[0031]FIG. 3 is a block diagram showing the construction of the controlsystem of the air conditioner according to this invention.

[0032] As shown in FIG. 3, the outdoor unit 1 includes an outdoorcontrol unit 13 and an outdoor communication circuit unit 14, inaddition to the variable capacity compressor 2, the PWM valve 3, and thefixed capacity compressor 4. The outdoor control unit 13 is connected tothe variable capacity compressor 2, the PWM valve 3, the fixed capacitycompressor 4, and the communication circuit unit 14 so as to transceivesignals with them. The outdoor communication circuit unit 14 tranceivesdata signals with the indoor units 9.

[0033] Each of the indoor units 9 includes an indoor fan 11, electricexpansion valve 12, indoor communication circuit unit 15, indoor controlunit 16, indoor temperature sensing unit 17, and a target temperaturesetting unit 18. The indoor control unit 16 is connected to the fan 11,electric expansion valve 12, indoor communication circuit unit 15,indoor temperature sensing unit 17, and the target temperature settingunit 18 so as to transceive signals with them. The indoor communicationcircuit unit 15 tranceives data signals with the outdoor unit 1.

[0034] The control unit 16 of each indoor unit 9 receives a presentindoor temperature sensed by the indoor temperature sensing unit 17 anda target temperature preset by the target temperature setting unit 18.Each of the indoor control units 16 stores the designed cooling capacityinformation of an associated indoor unit, and may calculate requiredcooling capacity of the indoor unit on the basis of a temperaturedifference between the present indoor temperature and the targettemperature, and the designed cooling capacity of the indoor unit.Alternatively, the indoor control unit 16 may calculate the requiredcooling capacity on the basis of the designed cooling capacity of theindoor unit exclusively. Signals, representing the required coolingcapacities calculated by the control units 16 of the indoor units 9, aretransmitted to the outdoor control unit 13 through the indoor andoutdoor communication circuit units 15 and 14.

[0035] Upon receiving the signals from the indoor control units 16, theoutdoor control unit 13 calculates the sum of the required coolingcapacities of the indoor units 9, and controls the operation of the twocompressors 2, 4 in accordance with the sum of the required coolingcapacities. When the sum of the required cooling capacities of theindoor units 9 does not exceed the capacity of the variable capacitycompressor 2, the outdoor control unit 13 operates only the variablecapacity compressor 2 while controlling the output of the compressor 2by outputting duty control signals to the compressor 2 in accordancewith a variation in the sum of the required cooling capacities. When thesum of the required cooling capacities of the indoor units 9 exceeds thecapacity of the variable capacity compressor 2, the outdoor control unit13 initiates the fixed capacity compressor 4 in addition to the variablecapacity compressor 2. In such a case, the outdoor control unit 13 alsocontrols the output of the variable capacity compressor 2 by outputtingduty control signals to said compressor 2 in accordance with a variationin the sum of the required cooling capacities of the indoor units 9.

[0036] During such a control operation of the outdoor control unit 13,the unit 13 may fail to smoothly operate the fixed capacity compressor 4if it directly starts the compressor 4 regardless of the operationalcondition of the variable capacity compressor 2 when the sum of therequired cooling capacities of the indoor units 9 increases to requirethe operation of the two compressors 2 and 4. That is, when the fixedcapacity compressor 4 is forcibly started at its inactivated state wherea large pressure difference exists between the high pressure side andthe low pressure side of the compressor 4, an excessive starting currentis induced and the starting performance of said compressor 4 is reduced.

[0037] When the fixed capacity compressor 4 is turned on to start at atime “ta” during a loading mode operation of the variable capacitycompressor 2 where refrigerant is discharged from said compressor 2 asshown in FIGS. 4a and 4 b, the total current “ic”, which is the sum ofthe starting current “ia” of the fixed capacity compressor 4 and theoperating current “ib” of the variable capacity compressor 2, quicklyincreases to exceed the maximum allowable current. Such a quick increasein the current prevents the smooth starting of the compressor 4, reducesthe starting performance of the compressor 4, and causes damage to thecompressor 4.

[0038] In order to overcome such a problem, the outdoor control unit 13starts the fixed capacity compressor 4 in consideration of theoperational condition of the variable capacity compressor 2 when it isrequired to start the compressor 4 due to an increase in the sum of therequired cooling capacities of the indoor units 9. In the presentinvention, it is preferable to design the outdoor control unit 13 suchthat it starts the fixed capacity compressor 4 during an unloading modeoperation of the variable capacity compressor 2, thus preventing aninduction of excessive starting current in the fixed capacity compressor4 and performing a smooth start of said compressor 4.

[0039] As shown in FIG. 5a, when the fixed capacity compressor 4 isrequired to start at a time “ta” during a loading mode operation of thevariable capacity compressor 2, the outdoor control unit 13 retards thestart of the compressor 4 for a predetermined period of time. In such acase, the “predetermined period of time” is the time consumed by thevariable capacity compressor 2 until the compressor 2 is converted fromthe loading mode into an unloading mode.

[0040] After the variable capacity compressor 2 is completely convertedfrom the loading mode into the unloading mode, the fixed capacitycompressor 4 is started under the control of the outdoor control unit 13at a time “tb”.

[0041] When it is required to start the fixed capacity compressor 4 eventhough the variable capacity compressor 2 maintains its loading modewith full capacity (100%) as shown in FIG. 5b, the outdoor control unit13 may retard the start of the fixed capacity compressor 4 for anexcessively lengthy period of time while waiting for a conversion fromthe loading mode of the compressor 2 to an unloading mode. In such acase, the starting of the fixed capacity compressor 4 is notaccomplished in a timely manner. Therefore, the outdoor control unit 13forcibly converts the loading mode of the variable capacity compressor 2into an unloading mode and maintains the unloading mode for apredetermined period of time “B” as shown in FIG. 5b when the fixedcapacity compressor 4 is required to start even though the variablecapacity compressor 2 maintains its loading mode operation with fullcapacity. The outdoor control unit 13 starts the fixed capacitycompressor 4 at a time “tc” after such a mode conversion.

[0042] In such a case, the “predetermined period of time B” ispreferably set to within one cycle of the duty control signal whichcontrols the variable capacity compressor 2, in an effort to quicklyattend to the restarting of the variable capacity compressor 2.

[0043] The “predetermined period of time B” is also preferably set inconsideration of the time required by the fixed capacity compressor 4 tooperate normally after the start.

[0044] The control operation of the outdoor control unit of the airconditioner according to this invention is described below withreference to FIG. 6.

[0045] Upon receiving signals representing the required coolingcapacities of the indoor units 9, the outdoor control unit 13 sums upthe required cooling capacities, and determines at step S101 whether itis required to operate the indoor units 9 in a cooling mode. When it isnot required to operate the indoor units 9 in a cooling mode, theoperation of the air conditioner is stopped at step S102.

[0046] When it is determined at step S101 that the indoor units 9 arerequired to be operated in a cooling mode, the outdoor control unit 13primarily operates the variable capacity compressor 2 at step 103, andcontrols the variable capacity of said compressor 2 in response to avariation in the sum of the required cooling capacities of the indoorunits 9.

[0047] During such an operation of the variable capacity compressor 2,the outdoor control unit 13 determines at step S104 whether it isrequired to start the fixed capacity compressor 4 due to an increase inthe sum of the required cooling capacities of the indoor units 9. Whenit is not required to start the fixed capacity compressor 4, theprocedure returns to step S101 so as to operate the air conditioner withthe refrigerant compressing capacity of only the variable capacitycompressor 2.

[0048] When it is determined, at step S104, that it is required to startthe fixed capacity compressor 4, the outdoor control unit 13 determinesat step S105 whether the variable capacity compressor 2 is in itsunloading mode. When it is determined that the variable capacitycompressor 2 is in its unloading mode, the outdoor control unit 13directly starts the fixed capacity compressor 4 at step S106, andreturns to the initial stage of the procedure.

[0049] When it is determined, at step S105, that the variable capacitycompressor 2 is not in its unloading mode, the outdoor control unit 13determines at step S107 whether the variable capacity compressor 2maintains its loading mode with full capacity. When it is determined, atstep S107, that the variable capacity compressor 2 does not maintain itsloading mode with full capacity, the outdoor control unit 13 returns tostep S105 and waits for a conversion of the operational mode of thevariable capacity compressor 2 from the loading mode into an unloadingmode, and starts the fixed capacity compressor 4 when the loading modeof the variable capacity compressor 2 is converted into an unloadingmode.

[0050] When it is determined, at step S107, that the variable capacitycompressor 2 maintains its loading mode with full capacity, the outdoorcontrol unit 13 forcibly converts the operational mode of the variablecapacity compressor 2 from the loading mode into an unloading mode for apredetermined period of time, and starts the fixed capacity compressor 4at step S108 prior to returning to the initial stage of the procedure.

[0051] Industrial Applicability

[0052] As described above, the present invention provides an airconditioner with a variable capacity compressor and a fixed capacitycompressor, and a method of controlling the operation of such an airconditioner. When it is required to start the fixed capacity compressordue to an increase in the sum of the required cooling capacities of theindoor units, the fixed capacity compressor is started during theunloading mode operation of the variable capacity compressor where thepressure difference between the outlet side and inlet side of thevariable capacity compressor is minimized. The fixed capacity compressoris thus smoothly started without causing an induction of excessivestarting current, and improves the operational reliability of the airconditioner.

[0053] Although the preferred embodiments of the present invention havebeen disclosed for illustrative purposes, those skilled in the art willappreciate that various modifications, additions and substitutions arepossible, without departing from the scope and spirit of the inventionas disclosed in the accompanying claims.

1. An air conditioner, comprising: a fixed capacity compressor withfixed refrigerant compressing capacity; a variable capacity compressoroperated in a loading mode for discharging refrigerant and in anunloading mode for ceasing to discharge refrigerant, with refrigerantcompressing capacity of the variable capacity compressor varying inresponse to a duty control signal which determines a loading time and anunloading time within a cycle; and a control unit starting the fixedcapacity compressor and the variable capacity compressor with adifference in time so as to prevent a synchronous start of said fixedcapacity compressor and the variable capacity compressor.
 2. The airconditioner according to claim 1, wherein said control unit starts thefixed capacity compressor after starting the variable capacitycompressor.
 3. The air conditioner according to claim 1, wherein saidcontrol unit starts the fixed capacity compressor such that a totalcurrent, which is the sum of a starting current of the fixed capacitycompressor and an operating current of the variable capacity compressor,does not exceed a maximum allowable current.
 4. The air conditioneraccording to claim 2, wherein said control unit starts the fixedcapacity compressor during an unloading mode operation of the variablecapacity compressor when it is required to start the fixed capacitycompressor.
 5. The air conditioner according to claim 2, wherein in thecase of the variable capacity compressor constantly maintaining aloading mode even though it is required to start the fixed capacitycompressor, said control unit forcibly converts the loading mode of thevariable capacity compressor into an unloading mode, and starts thefixed capacity compressor after the mode conversion.
 6. A method ofcontrolling an air conditioner consisting of a fixed capacity compressorwith fixed refrigerant compressing capacity, and a variable capacitycompressor being varied in refrigerant compressing capacity in responseto a duty control signal determining a loading time and an unloadingtime within a cycle, wherein the method comprises the steps of: startingsaid variable capacity compressor; determining whether it is required tostart the fixed capacity compressor in addition to an operation of thevariable capacity compressor; and starting the fixed capacity compressorin accordance with an operational condition of the variable capacitycompressor when it is required to start the fixed capacity compressor.7. The method according to claim 6, wherein the step of starting thefixed capacity compressor comprises the steps of: determining whetherthe variable capacity compressor is operating in an unloading mode; andstarting the fixed capacity compressor under the condition that thevariable capacity compressor is operating in an unloading mode.
 8. Themethod according to claim 6, wherein the step of starting the fixedcapacity compressor comprises the step of: starting the fixed capacitycompressor after waiting for a conversion in the operational mode of thevariable capacity compressor from a loading mode into an unloading modewhen the variable capacity compressor is being operated in the loadingmode.
 9. The method according to claim 6, wherein the step of startingthe fixed capacity compressor comprises the step of: starting the fixedcapacity compressor after forcibly converting an operational mode of thevariable capacity compressor from a loading mode into an unloading modewhen the variable capacity compressor is continuously operated in theloading mode.